Bcr-Abl, a constitutively activated tyrosine kinase resulting from the formation of the Philadelphia chromosome [Nowell P. C. and Hungerford D. A., Science 132, 1497 (1960)] by reciprocal translocation between the long arms of chromosomes 9 and 22 [Rowley J. D., Nature 243, 290-293 (1973)], has been established as the characteristic molecular abnormality present in virtually all cases of chronic myeloid leukemia (CML) and up to 20 percent of adult acute lymphoblastic leukemia (ALL) [Faderl S. et al., N Engl J Med 341, 164-172 (1999); Sawyers C. L., N Engl J Med 340, 1330-1340 (1999)]. Bcr-Abl is sufficient to cause CML in mice [Daley G. Q. et al., Science 247, 824-830 (1990)] and its transforming capacity is absolutely dependent on tyrosine kinase activity [Lugo T. G. et al., Science 247, 1079 (1990)]. The compound N-[4-methyl-3-(4-pyridin-3-yl-pyrimidin-2-ylamino)-phenyl]-4-(4-methyl-piperazin-1-ylmethyl)-benzamide (hereinafter also referred to as “STI571”; STI571 is described in EP-0 564 409 and, in the form of the methane sulfonate salt, in WO 99/03854), a competitive inhibitor at the ATP-binding site of Bcr-Abl, as well as of the receptor for platelet-derived growth factor, and c-kit tyrosine kinase [Lugo T. G. et al., Science 247, 1079 (1990)], has been shown to be capable of very rapidly reversing the clinical and hematological abnormalities of CML in chronic phase and in blast crisis as well as of Ph-chromosome-positive (Ph+) acute lymphoblastic leukemia (Ph+ ALL) [Druker B. J. et al., N Engl J Med 344, 1031-1037 (2001); Druker B. J. et al., N Engl J Med 344, 1038-1042 (2001)]. Whereas almost all chronic phase CML patients durably respond, remissions in CML blast crisis and Ph+ ALL are transient, and most patients relapse after several months, despite continued therapy with STI571 [Druker B. J. et al., N Engl J Med 344, 1038-1042 (2001)]. The mechanism of resistance to STI571 is subject of intense research.
I was now surprisingly found that mutations present in the kinase domain of the Bcr-Abl gene of patients suffering from CML or Ph+ ALL account for the biological resistance of these patients towards STI571 treatment in that said mutations lead to resistance of the Bcr-Abl tyrosine kinase towards inhibition by STI571.
These findings are extremely valuable in e.g. finding new compounds or combinations of compounds which are capable to overcome resistance towards treatment with STI571. Moreover, knowledge of such mutations is also very useful in the diagnosis of Ph+ leukemias in that it allows e.g. the detection of drug-resistant clones before clinical relapse of the patient.
Definitions:
Within the context of this disclosure the following expressions, terms and abbreviations have the meanings as defined below:                In the expression “a mutated functional Abl kinase domain”, the part “mutated Abl kinase domain” refers to the native human Abl kinase domain containing mutations including amino acid exchanges, amino acid deletions and/or amino acid additions.        In the expression “a mutated functional Abl kinase domain”, the term “functional” indicates that the respective kinase domain possesses tyrosine kinase activity. Preferably, the kinase activity of the mutated functional Abl kinase domain is in the range of that of the native human Abl kinase domain.        In the expression “a mutated functional Abl kinase domain being resistant to inhibition of its tyrosine kinase activity by STI571 or a salt thereof”, the term “resistant” means that STI571 inhibits the respective mutated functional Abl kinase domain with an IC50 that is higher than that of the native human Abl kinase domain, i.e. higher than about 0.025 μM, preferably higher than about 0.15 μM, more preferably higher than about 0.25 μM, most preferably higher than about 5 μM.        In the expression “amino acid sequence of the native human Abl kinase domain or an essentially similar sequence thereof”, the part “or an essentially similar sequence thereof” refers to the amino acid sequence of the native human Abl kinase domain containing mutations, including amino acid exchanges, amino add deletions and/or amino acid additions, that are not essential for the functionality of the kinase and its resistance to inhibition by STI571 or a salt thereof within the meaning of the term “functional” and “resistant” as defined hereinabove.        The expression “replaced by another amino acid” refers to the replacement of a certain natural amino acid by another natural amino acid.        The names of the amino acids are either written out or the one letter or three letter codes are used. Mutations are referred to by accepted nomenclature, e.g. “Ala380Thr” or “380 Ala→Thr” both indicating that alanine at position 380 is replaced by threonine.        SEQ ID NO:1 represents the cDNA coding for the native human Abl protein (human c-abl mRNA; GenBank Accession No.: X16416).        SEQ ID NO:2 represents the amino acid sequence of the native human Abl protein (human c-Abl; SwissProt Acc. No.: P00519).        Unless indicated otherwise, the number given for a certain amino acid refers to the numbering of the amino acids in SEQ ID NO:2. In an amino acid sequence that is essentially similar to the amino acid sequence of the native human Abl kinase domain within the meaning as defined above, the amino acids are numbered in accordance with the numbering of the amino acids in SEQ ID NO:2.        The term “isolated” means that the material is removed from its original environment (e.g., the natural environment if it is naturally occurring).        A “host cell”, refers to a prokaryotic or eukaryotic cell that contains heterologous DNA that has been introduced into the cell by any means, e.g., electroporation, calcium phosphate precipitation, microinjection, transformation, viral infection, and the like.        